(1) Field of the Invention
The present invention relates to an improvement of the tread profile of heavy duty pneumatic radial tires for use in heavy duty vehicles such as trucks and buses to obviate shoulder drop uneven wear and railway wear of the tires.
(2) Related Art Statement
In heavy duty pneumatic radial tires used in heavy vehicles such as trucks and buses, a shoulder drop uneven wear frequently occurs on outer sides of tires mounted (hereinafter referred to as "mounted tire outer sides") at front wheels. When this is attempted to be avoided, railway wear called river wear disadvantageously tends to occur.
The profile of treads of heavy duty pneumatic radial tires is generally designed in a bilaterally symmetrical shape. In such a case, the above-mentioned shoulder drop uneven wear frequently occurs at outer sides of the front wheel tires of the vehicle. To cope with this problem, a ground contact pressure at shoulder portions of the tread is increased by enlarging a crown radius, that is, a radius of curvature of a tread contour curve. However, wearing degree differs between a side on which the tire is mounted to the vehicle (hereinafter referred to as "mounted tire inner side") and the mounted tire outer side due to a difference in a reaction force at a time of ground contacting therebetween, so that a satisfactory effect can not be obtained.
Although an asymmetrical radius type crown in which the radius of curvature is made large on the mounted tire outer side than that on the mounted tire inner side with respect to a tire equator is described in Japanese patent application Laid-open No. 179,304/1985. However, while this technique is advantageous to reduce shoulder drop uneven wear, the ground contact pressure of a rib adjoining to the shoulder rib tends to lower, thereby readily resulting in river wear.
As the case may be, a so-called one side wear by which only the mounted tire outer side is worn takes place depending upon running conditions. In addition, wondering (a phenomenon that a handle is caught when a vehicle is running along an inclined surface such as a rotted road) performance is damaged.